Selectivity, also commonly referred to as coordination and discrimination, is the ability of a power distribution system to prevent current flow to downstream loads with protection from a downstream device (e.g., a circuit breaker) while maintaining current flow through an upstream device and other loads associated with the upstream device. A power distribution system may contain a series of circuit breakers, namely upstream breakers and downstream breakers. When circuit breakers are connected in series, it is desirable to ensure that a given fault caused by a short circuit condition will trip the circuit breaker closest to the fault. Such selectivity permits downstream circuit breakers connected in series with upstream circuit breakers to trip without also tripping any upstream breakers. In this way, current to a room in a building can be shut off without shutting off current to the entire building. However, the upstream breaker must also be able to provide adequate protection for the circuit breaker when operating standalone in a non-selective application. If an upstream device trips at too low of a current threshold, there is no selectivity with any downstream breakers. If the upstream device trips at too high of a current threshold, there might not be adequate protection for the circuit breaker or its electrical system. Further, any tripping system must also ensure protection for the circuit breaker and the system in the event of a single-phase condition, e.g. only one phase becomes overloaded. Existing selectivity systems for use with circuit breakers are expensive to implement because all the circuit breakers within the system require the use of an electronic trip unit. This increases the cost of the entire system because of the cost of each individual circuit breaker and because of the effort required in coordinating the trip units of the circuit breakers.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a sensor for a power distribution system in which the sensor includes: a conductor; a core located proximate the conductor; and a reed switch adjacent the core, the reed switch in electrical communication with an electronic trip unit.
In an alternative embodiment, a power distribution system includes: an upstream circuit breaker including an electronic trip unit; a downstream circuit breaker in electrical communication with the upstream circuit breaker; a first sensor positioned downstream from the downstream circuit breaker, the first sensor includes: a conductor in electrical communication with the downstream circuit breaker; a core located proximate the conductor; and a reed switch adjacent the core, the reed switch in electrical communication with the electronic trip unit.